It’s getting hot in here: Reptile assemblages in drought-affected forest

By Shannon Dundas. In the past 50 years, the climate in southwest WA has become hotter and drier [1, 2]. Annual rainfall in the northern jarrah forest has decreased by 17% since the 1970s [3].  In addition to the direct effects, changing climate is having a substantial impact on wildlife species through changes in habitat.

Southwest WA has a typical Mediterranean climate: hot, dry summers and cool, wet winters. Native plants in this region can withstand months of summer drought by using soil water stores that are replenished by predictable winter rainfall. More recently, longer summers and winters with less rainfall each year have depleted soil water stores, which are no longer being completely recharged.

In the past 10 years, three drought periods in the northern jarrah forest have occurred (2001, 2006 and 2010). The most recent event resulted in the death of mature jarrah trees (Eucalyptus marginata) leaving patches of forest with open canopies (Fig. 1) [4]. I compared reptile communities within these open canopy drought sites with equivalent healthy sites.

Fig. 1 Drought affected jarrah (Eucalyptus marginata) forest

Trapping was carried out during summer 2013/2014, 3 years after the 2010/2011 summer drought event. In response to the drought, mature trees had shed their leaves and some had died, resulting in a thick cover of leaf litter at these sites. Three years on, the leaf litter had degraded but was not being replaced, resulting in large areas of exposed ground in drought sites.

Reptiles were sampled using a comparative technique of pitfall trapping and camera trapping. Monthly surveys were carried out over 5 months at 8 drought sites, each with a paired healthy site located within 1km in the same vegetation type.

Overall species richness of reptiles did not differ between drought affected and intact sites; however, grouping species by preferred habitat niche, small litter-dwelling skinks (including Lerista distinguenda, Morethia obscura and Acritoscincus trilineatus) were captured less frequently in drought affected sites. Conversely, the western bearded dragon (Pogona minor; Fig. 2) was captured more frequently in drought affected sites.

Fig. 2 The western bearded dragon (Pogona minor) is an arboreal species that uses standing and course woody debris

To explore differences in reptile microhabitat, iButtons® were placed in five locations (on logs, in logs, on trees, under vegetation and on open ground) at four drought sites and four healthy sites during February and March (Mean daily temperature February 30.5°C, March 27.8°C; 5). Microhabitats in drought-affected sites were hotter compared to those in healthy sites. During February, the maximum daily temperature logged at a drought site on open ground exceeded 50°C every day for 4 weeks. The open microhabitat in the paired healthy site was on average 4.2°C cooler than the drought site. These high temperatures in the jarrah forest, coupled with restricted summer rainfall (Mean monthly rainfall January 12.8mm, February 15.1mm; BOM, 2015) make these sites an extreme environment for both plants and animals.

Over time, it is likely reptile assemblages in drought sites will shift as the habitat changes. Drought sites lack suitable refuge for litter-associated species but provide abundant course woody debris which will benefit species using log piles and dead standing trees, at least in the short term. For plants, such extreme conditions may restrict the growth and survival of new seedlings and limit natural regeneration within these areas.

Literature cited

  1. Petrone, KC, JD Hughes, TG Van Niel, and RP Silberstein, Streamflow decline in southwestern Australia, 1950-2008. Geophysical Research Letters, 2010. 37(11): p. L11401 1-7.
  2. Hughes, JD, KC Petrone, and RP Silberstein, Drought, groundwater storage and stream flow decline in southwestern Australia. Geophysical Research Letters, 2012. 39(3): p. L03408 1-6.
  3. Standish, RJ, MI Daws, AD Gove, RK Didham, AH Grigg, JM Koch, and RJ Hobbs, Long-term data suggest jarrah-forest establishment at restored mine sites is resistant to climate variability. Journal of Ecology, 2015. 103(1): p. 78-89.
  4. Matusick, G, KX Ruthrof, NC Brouwers, B Dell, and GSJ Hardy, Sudden forest canopy collapse corresponding with extreme drought and heat in a mediterranean-type eucalypt forest in southwestern Australia. European Journal of Forest Research, 2013. 132(3): p. 497-510.
  5. BOM. Bureau of Meteorology. 2015; Available from: http://www.bom.gov.au/.

For more information, contact Shannon Dundas S.Dundas@murdoch.edu.au

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